1. Field of the Invention
The present invention relates to a system and method for diagnosing a state of cooling water, and more particularly, to a system and method for diagnosing a state of cooling water capable of determining a state of plumbing with application of load model of the cooling water plumbing even under a condition that a cooling water pump speed changes.
2. Description of the Related Art
A fuel cell system mounted in a fuel cell vehicle is configured with a hydrogen supply system that supplies hydrogen to a fuel cell stack; an air supply system that supplies oxygen, which is an oxidizing agent necessary for an electrochemical reaction, in the air to the fuel cell stack; the fuel cell stack that generates electricity based on the electrochemical reaction of the hydrogen and oxygen; and a heat and water management system that removes an electrochemical reaction heat from the fuel cell stack and simultaneously, adjusts temperature of the fuel cell stack.
The heat and water management system includes a cooling water pump that circulates cooling water to the fuel cell stack, and a radiator that cools the cooling water discharged from the fuel cell stack after cooling, and also includes an ion filter that filters ions flowing out from a cooling loop. An atmospheric pressure cap is mounted on the top end of the radiator of the heat and water management system, a reservoir is provided in an atmospheric structure, and a water level sensor is mounted in the inner side. A predetermined package space is necessary for mounting the water level sensor for the cooling water in the reservoir, but it may be difficult to secure the package space. In addition, even when the water level sensor is mounted therein, when the cooling water is mixed with the air and circulated, the water level sensor is not capable of detecting a loss of the cooling water and may continuously perceives the water level as normal.
In other words, a cooling water shortage phenomenon may be determined through the water level sensor or a pressure sensor installed in the plumbing, but such a method frequently results in misdetection by the sensor due to an influence of disturbances such as a temperature change in cooling water, a cooling loop change due to opening or closing of a cooling line valve, or vibration of a vehicle or equipment, etc. Accordingly, a flow rate sensor may be mounted in the cooling water plumbing. However, the mounting of the flow rate sensor may be complex, since the sensor is expensive and it is not convenient to install separate plumbing to mount the sensor therein.
In order to address limitations in the cooling water determination method as the above-described sensor manner, the applicant of the present invention has proposed a technique for determining whether the cooling water is normally circulated through an analysis of torque (i.e. current) or an output of the cooling water pump. However, the related art also enables the determination for the normal circulation of the cooling water only in a normal state period in which a cooling water pump speed is constant. In an actual system, since the cooling water pump speed is variably controlled in real time based on a heat amount, there is a limitation in determination of the cooling water state only with determination of normal circulation of the cooling water at a fixed speed.
The matters described as the background arts are merely intended to increase the understanding of the background of the present invention, and should not be recognized as being prior arts which are already known to those skilled in the art.